In one method of finishing a surface, an abrasive disk is fitted to a rotating shaft of a power tool. The power tool rotates the disk which is urged against the surfaced to be finished. The rotating disk has an abrasive surface which contacts and prepares the surface as desired by the user. As an example, a power tool such as a grinder, may be fitted with such an abrasive wheel to prepare pipe surfaces before welding on those surfaces.
One type of grinding disk, a flap disk, includes a backing plate and a series of flexible, overlapping, abrasive flaps attached to an outer periphery of the backing plate. The flaps are usually made from a cloth material which includes either an aluminum oxide grain or a zirconium-aluminum oxide grain adhered to the surface of the cloth material. The flaps are the primary surface preparation medium and the backing plate provides a structure on which to support the rotating flaps. U.S. Pat. Nos. 5,752,876 and 6,945,863 disclose similar flap disk wheels and their disclosures are incorporated by reference herein in their entirety.
As the flaps wear away during use, a portion of the backing plate may come into contact with the work piece. As a result, the abrasive disk works most effectively when the backing plate also wears as it contacts the work piece. Furthermore, the backing plate must transfer (i.e., without breaking) a load applied by the user from its inner diameter where the backing plate is secured to its outer diameter to which the flaps are secured. In other words, the backing plate must be composed of a material capable of withstanding normal internal operational stresses without breaking while, at the same time, it must be composed of a sufficiently wearable material.
Fiberglass is a material used to strengthen backing plates. Specifically, fiberglass (e.g., woven or nonwoven) can be positioned to absorb tensile loads experienced in a backing plate. However, in some applications, fiberglass does not wear cleanly. Resin-abrasive mix, which is also used in wearable back plates, on the other hand, wears cleanly, but does not have sufficient strength for some applications. There is therefore a need to develop a backing plate structure that wears at about the same rate as the flaps and that wears cleanly.